1. Field of the Invention
The present invention relates to a liquid crystal display device. More particularly, the present invention relates to a liquid crystal display device having a light leakage preventing structure in a periphery of an active region.
2. Description of the Related Art
A liquid crystal display device (LCD) has low power consumption and good portability. Also, the LCD is considered as a next generation display device having high added value.
In the LCD, liquid crystals are injected between two substrates in which transparent electrodes are formed and images are displayed using anisotropy of the liquid crystals according to a difference of refractive indexes.
Recently, an active matrix LCD (hereinafter, simply referred to as LCD) has better resolution and moving image reproducibility and thus is most spotlighted. The active matrix LCD includes a plurality of switching thin film transistors that can control the on/off of voltage according to pixels.
FIG. 1 is a sectional view of a related art LCD.
In FIG. 1, the related art LCD includes an upper substrate (a color filter substrate) 12, a lower substrate (an array substrate) 14, and a liquid crystal layer 16. The upper substrate 12 is arranged opposite the lower substrate 14, and the liquid crystal layer 16 is interposed between the upper substrate 12 and the lower substrate 14.
An active region Ia containing a pixel region P is defined in the lower substrate 14, and a first non-active region Ib is defined in an outer periphery of the active region Ia. A second non-active region Ic is defined in the upper substrate 12. The second non-active region Ic is located at a position that is more inside the active region Ia than the first non-active region Ib corresponding to the lower substrate 14.
A thin film transistor T is formed on the active region Ia of the lower substrate 14. The thin film transistor T includes a gate electrode 18, a semiconductor layer 22, and source and drain electrodes 24 and 26. Also, a pixel electrode 32 connected to the thin film transistor T is formed on the pixel region P.
A color filter layer 34, a planarization layer 38, and a common electrode 40 are sequentially formed on the upper substrate 12. At this time, the color filter layer 34 includes a black matrix 34a and a color filter 34b. The black matrix 34a is formed over the thin film transistor T and the second non-active region Ic, and the color filter 34b partially overlaps the black matrix 34a and includes red (R), green (B) and blue (B) colors that are repetitively formed on the pixel region P.
Although not shown in FIG. 1, upper and lower alignment layers are formed in an inner surface of the upper and lower substrates 12 and 14 contacting the liquid crystal layer 16.
A spacer 42 is formed inside the liquid crystal layer 16 so as to constantly maintain a cell gap between the upper and lower substrates 12 and 14. In order to maintain the cell gap and prevent leakage of the liquid crystal layer, a seal pattern 44 is formed in an outer periphery of the active region Ia between the upper and lower substrates 12 and 14.
In order to connect an external circuit and the LCD, a data pad part II is formed at an end portion of data line 25, which is integrally formed with the source electrode 24 of the thin film transistor T, in the first non-active region Ib of the lower substrate 14.
Upper and lower polarizers 31 and 35 are respectively attached on outer surfaces of the upper and lower substrates 12 and 14, and a backlight is disposed at a lower portion of the lower polarizer 35 so as to supply an additional light source.
In such an LCD, the black matrix 34a is formed in the non-active region, except the thin film transistor region and the color filter 34b. Therefore, it is possible to effectively shield the light source LI corresponding to the non-active region in the periphery portion of the seal pattern 44 and to prevent a lightening phenomenon at a periphery of a screen.
The black matrix 34a is formed of a metal thin film such as Cr having an Optical Density (OD) of 3.5 or more, or carbon-based organic material, or a photo-acryl resin. A dual-layer structure of Cr/CrOx may also be used for the purpose of low reflection of the screen.
However, when the black matrix 34a is formed of a metal such as Cr, low resistance results in a leakage current. This causes distortion of an electric field and affects an image. Thus, it is preferable to use a resin black matrix that can prevent the leakage current because of its high resistance. A specific resistance of the resin black matrix 34a is about 107 Ω.
However, the resin black matrix has different transmittance characteristics in wavelengths of incident light according to the manufacturing methods of the resin black matrix. The transmittance characteristics are determined by the OD (Optical Density) characteristic that is an ability to shield light.
In recent years, the LCD is becoming larger and the backlight is also becoming larger and brighter. However, when such a high brightness model, that is, high-brightness beam of 5000 nit or more, is supplied to the LCD panel, the resin black matrix 34a has an OD value that is changed by a transmittance characteristic, as described above. Thus, the beam cannot be effectively shielded.
In addition to the related art TN LCD shown in FIG. 1, a related art In-Plane Switching (IPS) LCD and a Thin film transistor On Color filter (TOC) LCD or a Color filter On Thin film transistor (COT) LCD where the color filter layer and the array element are formed together on the lower substrate cannot overcome the above problems.